An electrical transformer is a component that consists of two or more coils which are coupled together by magnetic induction, and which is used to transfer electric energy from one or more circuits to one or more other circuits, without change in frequency but usually with changed values of voltage and current. Typically, such a transformer is installed to the top portion of the ground-standing poles supporting electrical lines, beneath the high-voltage lines, near houses. Indeed, high voltage current is more efficient where transport of electricity over long distances is required, yet, lower voltage is required for domestic use, hence the need of such transformers.
These transformers are very heavy, and it is not an obvious task for the utility company workers to install this component to the top of the upright pole. Usually, this is done with a crane provided with a power hoisting gear, coupled to a cable depending from the crane boom. The problem oft encountered is in the way the cable is releasably secured to the transformer body. Indeed, the transformer has an outer housing of smooth, cylindrical shape with transverse sling hooks conventionally provided integrally to the housing, for releasable anchoring of the crane sling cable. It is essential that the transformer be firmly and tightly secured by the cable during its lifting to the top of the pole, yet be easily and quickly released after bolting to the pole body. It is easy to understand the health hazard to the utility workers beneath or around the transformer, should the very heavy transformer accidentally (brutally) release during lift and fall to the ground: lethal impact on the ground, or crane cable whiplash that would hurt the workers around the upstanding transformer and perhaps drive these workers toward and in contact with live, high-voltage electrical lines--another lethal accident. Yet, such accidental disconnection of the crane cable from the transformer is not uncommon, particularly with wear associated with extensive use of the sling. This is because the sling cable tends in use to shear against the top circular rim edge of the cylindrical transformer, particularly so when the transformer sways laterally during lift due to wind or other conditions. Such concern as to cable shearing action is increased by the fact that transformers are not of uniform dimensions (particularly not of uniform diameter) or weight When a cable sling is used for lifting different types of transformers, it will tend not to hold as tightly and as firmly the transformer, when the latter is of relatively small dimensions, or will tend to shear more against the top rim edge, when the transformer is of relatively large dimensions.
U.S. pat. No. 3,010,751 to Day and Berg, and U.S. pat. No. 3,549,190 to Caldwell, each shows a cable sling consisting of a transverse compensation bar provided with load body securing members at its two opposite ends, and means to manually adjust the relative position of the securing members accordingly with the dimensions of the hoisted load. It is understood that one has to manually adjust the sling, each time a new load needs to be connected thereto and lifted--a tedious operation. Moreover, because of the heavy load sustained due to the weight of the heavy hoisted load, there are concerns that the releasable manual locking means (pawl 19 in Day, stopper means 24 in Caldwell) may accidentally release due to sudden jolt associated with unexpected hoist gear pulling speed variations or varying wind conditions. This again would constitute hazardous conditions for the workers.